Animals and plants rely on pattern recognition receptors (“PRRs”) to detect conserved microbe-associated molecular patterns (“MAMPs”) in potential pathogens (Zhang et al., “Plant Immunity Triggered by Microbial Molecular Signatures,” Mol Plant 3:783-793 (2010)). Two well understood peptide MAMPs, flg22 and flgII-28, are derived from flagellin, which forms the ‘tail’ bacteria use for motility (see FIG. 1 of Gomez-Gomez et al., “Flagellin Perception: A Paradigm for Innate Immunity,” Trends Plant Sci 7:251-256 (2002)). In humans, the Toll-like receptor 5 (TLRS) binds a flagellin-derived MAMP that involves a peptide region known as flgII-28 thereby activating innate immunity. In plants, the best-characterized PRR is FLS2 that binds flg22. FLS2, which is conserved in monocots and dicots, is a leucine-rich repeat (“LRR”) receptor-like kinase (“RLK”) that activates pattern-triggered immunity (“PTI”) (Gomez-Gomez et al., “FLS2: An LRR Receptor-like Kinase Involved in the Perception of the Bacterial Elicitor Flagellin in Arabidopsis,” Mol Cell 5:1003-1011 (2000)). Tomato and other species in the family Solanaceae, but not Arabidopsis and other plants, recognizes flgII-28 (Cai et al., “The Plant Pathogen Pseudomonas syringae pv. tomato is Genetically Monomorphic and Under Strong Selection to Evade Tomato Immunity,” PLoS Pathogens 7:e1002130 (2011)). This finding is significant because some pathogens have a divergent flg22 region that allows them to evade detection by FLS2 (Sun et al., “Within-species Flagellin Polymorphism in Xanthomonas campestris pv. campestris and Its Impact on Elicitation of Arabidopsis FLAGELLIN SENSING2-dependent Defenses,” Plant Cell 18:764-779 (2006), which is hereby incorporated by reference in its entirety). The existence of a PRR that recognizes flgII-28 may therefore allow tomato and other plant species to recognize a broader range of bacterial pathogens.
Importantly, PRRs can be transferred from one plant species to another and remain functional. For example, the Arabidopsis receptor EFR, which recognizes the bacterial MAMP elongation factor (“EF”) Tu, was transformed into tomato and N. benthamiana, which are normally unable to detect EF-Tu. (Lacombe et al., “Interfamily Transfer of a Plant Pattern-Recognition Receptor Confers Broad-spectrum Bacterial Resistance,” Nat Biotechnol 28:365-369 (2010)). It was shown that the EFR-expressing plants were resistant to previously virulent pathogens (Lacombe et al., “Interfamily Transfer of a Plant Pattern-Recognition Receptor Confers Broad-spectrum Bacterial Resistance,” Nat Biotechnol 28:365-369 (2010)). Other recent examples include the transfer of the ReMAX PRR from Arabidopsis to tobacco and the expression of the tomato Ve1 gene in Arabidopsis (Jehle et al., “The Receptor-Like Protein ReMAX of Arabidopsis Detects the Microbe-Associated Molecular Pattern eMax from Xanthomonas” Plant Cell 25(6):2330-2340 (2013) and Fradin et al., “Interfamily Transfer of Tomato Ve1 Mediates Verticillium Resistance in Arabidopsis” Plant Physiol 156(4): 2255-2265 (2011)). In both cases, the genes provided new recognition specificity.
Significant agricultural benefits may arise from the identification of PRRs that occur in only some plant species. Such species-specific PRRs can be used to broaden and enhance disease resistance when transferred into economically important and taxonomically diverse plants that do not naturally express them (see Lacombe et al., “Interfamily Transfer of a Plant Pattern-Recognition Receptor Confers Broad-spectrum Bacterial Resistance,” Nat Biotechnol 28:365-369 (2010)). Despite this potential, there are few cloned PRR genes available from plants and the majority of these are widely conserved, so they do not offer the possibility of interspecies transfer. Further, despite progress in understanding the genetic control of plant resistance to pathogens, little progress has been reported in the identification and analysis of key regulators of pathogen resistance. Characterization of such genes would allow for the genetic engineering of plants with a variety of desirable traits.
The present invention is directed to overcoming these and other deficiencies in the art.